Pre-heat the oven to 375°F.
Whisk together the flour, cocoa, salt and baking soda. Beat the butter on medium speed for about 1 minute, until smooth. Add the sugars and beat for another 2 minutes or so, until well blended. Add the peppermint extract. Add the eggs, one at a time and beat until blended. Add the dry ingredients, mixing only until just incorporated. Add the chocolate chips.
Drop rounded tablespoonfuls on baking sheets lined with parchment paper, leaving about 2 inches between each cookie, and bake for 10-12 minutes.